Saimiri sciureus, the squirrel monkey is a South American or New World monkey. South American monkeys or platyrrhines comprise one of the two infraorders (Platyrrhini and Catarrhini) of anthropoid primates. They live exclusively in South and Central America, but their fossil distribution includes the Greater Antilles (MacPhee and Horovitz, 2002). The fossil record of platyrrhines extends back to the Deseadan or late Oligocene of Bolivia where they are represented by the genus Branisella (Takai and Anaya, 1996). Their presence in the New World is generally considered to be the result of a single dispersal event (Fleagle, 1999) near the end of the Eocene from the Old World, where all known basal anthropoids are found (Beard, 2002). Because South America was not connected with North America or Africa at the time, this dispersal must have involved rafting across some portion of the Atlantic.

Once in the New World, platyrrhines diverged into a variety of forms ranging in size from the smallest living anthropoid (Cebuella) at ~110 grams to the howler monkeys (Alouatta) that reach 11 kg (Fleagle, 1999). This diverse radiation of primates includes 78 living species (Fleagle, 1999) in 16 genera, one of which is the only living nocturnal anthropoid, Aotus. Their diets and locomotor adaptations are diverse, though most are at least partly frugivorous and none are primarily terrestrial.

Although the adaptations of different genera are reflected in their craniodental anatomy, platyrrhines in general retain a cranial morphology more similar to primitive anthropoids from the Eocene and Oligocene of Egypt such as Catopithecus, Parapithecus, and Aegyptopithecus than do the living Old World anthropoids (Fleagle, 1999; Simons, 2001). The research for which these CT data were collected indicates that this primitive anthropoid cranial morphology included considerable cranial pneumatization via the paranasal sinuses.

Saimiri sciureus is among the smaller platyrrhines, males and females averaging 779g and 668g respectively (Fleagle, 1999). Despite its smaller size, it is closely related to Cebus (Horovitz, 1999; Rosenberger, 2002). Note the close approximation of their orbits. In adults the interorbital septum is fenestrated such that the eyes are separated by only membrane. Saimiri is largely frugivorous, but forages for insects when on the ground (Fleagle, 1999).

About the Species

This male specimen, the skull of a juvenile (M3 erupting), was collected in Brazil on 27 January 1948. It was made available to The University of Texas High-Resolution X-ray CT Facility for scanning by Dr. James Rossie of Stony Brook University, courtesy of the Smithsonian Institution Division of Mammals. Scanning was funded by an NSF dissertation improvement grant to Mr. Rossie (#0100825). Funding for image processing was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin.

lateral view

dorsal view

About this Specimen

This specimen was scanned by Matthew Colbert on 6 March 2002 along the coronal axis for a total of 512 slices. Each slice is 0.1189 mm thick, with an interslice spacing of 0.1189 mm and a field of reconstruction of 52.0 mm.